Geons (geometric ions) are simple 3-dimensional forms such as spheres, cubes, cylinders, cones or wedges. One often-cited[1] theory of object recognition, Biederman's recognition-by-components (RBC)[2] theory, proposes that visual input is matched against structural representations of objects in the brain. These structural representations consist of geons and their interrelations (e.g., an ice cream cone could be broken down into a sphere located above a cone). Geons can be used to represent a large number of possible objects with very few components; e.g., 24 geons can be recombined to create over 10 million different two-geon objects.

Some more recent studies[3] suggest three-dimensional object recognition is viewpoint dependent, rather than independent, in refute of recognition-by-components theory and geons. This refute follows in part from the observation that different regions of the brain respond to different viewpoints of a common object, say, the human face. Since each region responds differently to different viewpoints of the same human face, the brain must not use a common underlying geon-based schema for image recognition, instead relying on a viewpoint-dependent encoding schema where matches are determined by similarity.